Often, in fanfiction, Snape's liking for Harry is portrayed in his internal thoughts. The author might write from Snape's perspective, showing how he admires Harry's courage and how it reminds him of Lily. There could also be moments where Snape defends Harry in front of other characters, which is a clear sign of his positive feelings for Harry. And sometimes, he might even share personal stories or advice with Harry, which is a big step considering their relationship in the original story.